94 mustang gt 5.0 5 speed rpm issue

[bethlewallen]

Hi
I have a 94 gt 5.0 5 speed. I'm having an issue with the rpms when I push in the clutch. The rpms don't go down while the clutch is pushed in. When I shift up in gears the rpms don't go down or if they do very slowly. While down shifting the rpms do as they should.... I have changed the tps and it still does the same thing. Anybody have any ideas what could be wrong? any info is helpful!!!

[HiFlow5 0]

When you changed the TPS, did you properly set the voltage back to factory specs? This could result in a rev'ig as you mentioned. Clogged up IAC and dirty throttle body could also result in this as well. What RPM's is the motor rev'ing to when you depress the clutch? A vacuum leak could also cause the same issue you described.

I would first start by making sure the TPS was set properly with the correct voltage. I have a write up on this in the tech section if you do not know how to check the voltage. I would then remove and clean the IAC with carb cleaner and also spray the throttle body as well. I would then check for vacuum leaks to ensure no un-metered air is entering the engine. You may need to buy a vacuum gauge for this.

[bethlewallen]

What is the IAC? Sorry if this is a dumb question. I'm a girl so I don't know all the abbrevations.

[Blue)(Fusion]

IAC = Idle Air Control valve. It is mounted on the back of the intake plenum. It will have a small air tube running to it and it is mounted with two 10mm bolts. It's easy to remove and re-install. Just be sure to not tear the gasket.

Also, why should the RPMs drop when the clutch pedal is depressed? With the clutch depressed or it's not in any gear, the RPMs should be roughly 800 RPM, IIRC.

And don't worry too much about being a girl with tech stuff. Most guys don't know what they mean either

[bethlewallen]

Well we checked all that stuff! And still does it. The tps is at .95. We replaced it IAC. We cleaned the throttle body. The rpms just stay at whatever rpm it was at when I go to shift up in gears. If you shift fast it isn't as noticable. I guess I'm just gonna have to shift fast and forget about it.

[Blue)(Fusion]

So let me clarify. You are in, say, 2nd gear shifting to 3rd gear but when you shift and let off the clutch the RPMs are higher than what they should be for that gear at your current road speed?

What's the condition of the clutch?

[serge_saati]

I think it's a problem with the MAF sensor (mass air flow) sensor. When it doesn't detect the sensor, it can't adjust air fuel mixture, so it goes in default mode. So the mixture is alway the same. So rpm can't decrease enough. You can check the sensor.

when you shift up, release the clutch very slowly. if not, it'll jerk a lot.

[bethlewallen]

No its kinda hard to explain. Say I'm in second gear and going to shift into third gear and its at 4500 rpm while the clutch is pushed in and I am ready to shift into the third gear the rpms stay at 4500. Then once u are in third gear the rpms will then drop as it should. I just know that in my dodge stratus when I push in the clutch even before I go into a higher gear the rpms will drop just a bit then drop more when I get into the next gear. So I guess the rpms sorta freezes in my mustang until I get into the next gear. Does that make any sense?

[serge_saati]

Yes I understand what you mean the first time. I know there's a problem with your car.
I just say until you repair the problem, you should release clutch slower as usual. Cause when you release the clutch, the rpm will forced to drop naturally. So if you release it too quick, it will drop too quick.

I said that the problem can be related to MAF sensor or PCM. When you release the gas with clutch depressed, air/fuel mixture should be leaner to forces the engine to slow down. If you have problem with these parts, engine cannot tune its mixture, so it's possible that it cant slow down. Cause engine has enough horse power to naturally keep its rpm when you release the gas. The purpose of the computer in this case is to artificially reduce rpm when you release the gas at idle then stabilize it.

Try to disconnect the MAF sensor to see if something change. If nothing change, then the problem is definitively the MAF.

[zinda89]

have an '89 that did this exact same thing -push in clutch RPM's go up to 2k or so, makes for hard mountain driving as was my case. I'll tell you now that it took me almost 2 years of it coming snd going with everybody suggesting all kinds of high dollar parts replacement and tricky vacuum/ electrical type measuring ohm and volt values while engaging or disengaging of every little part 1 could imagine, wrong! It's simply a matter or very closely examining all of the vacuum lines that become very brittle after a few hundred thousand miles my case 275k for now till I rebuild the tranny. When I say closely I mean it ! mine was a tiny hairline crack running along the length of a tube all of 1/4" in length, the reason it came and went was due to the shacking around of the car and motor leaving the crack opened up more or not at all. I did replace a few of the lines with simply putting windshield washer hose pieces over the areas I thought the cracks were. It seemed like it did it but nope just as un predictable as it was it would return over and over until I ripped out the clump of 4 or so plastic lines that all joined together at a square 5 or so to 1 type connection 1 had a cap on the unused nipple. this is how I saw it because now I could see it from every angle under a lighted magnifying glass and done fixed! 2 weeks later my transmission bites it and that was 3 years ago I still say I'm going to fix the tranny but in the mean time have a 2002 GT to drive until I'm in the mood to start that job. I'm sure that I'll get to it before I need to replace the 2002 with a newer model but only time will tell.

[zinda89]

have an '89 that did this exact same thing -push in clutch RPM's go up to 2k or so, makes for hard mountain driving as was my case. I'll tell you now that it took me almost 2 years of it coming snd going with everybody suggesting all kinds of high dollar parts replacement and tricky vacuum/ electrical type measuring ohm and volt values while engaging or disengaging of every little part 1 could imagine, wrong! It's simply a matter or very closely examining all of the vacuum lines that become very brittle after a few hundred thousand miles my case 275k for now till I rebuild the tranny. When I say closely I mean it ! mine was a tiny hairline crack running along the length of a tube all of 1/4" in length, the reason it came and went was due to the shacking around of the car and motor leaving the crack opened up more or not at all. I did replace a few of the lines with simply putting windshield washer hose pieces over the areas I thought the cracks were. It seemed like it did it but nope just as un predictable as it was it would return over and over until I ripped out the clump of 4 or so plastic lines that all joined together at a square 5 or so to 1 type connection 1 had a cap on the unused nipple. this is how I saw it because now I could see it from every angle under a lighted magnifying glass and done fixed! 2 weeks later my transmission bites it and that was 3 years ago I still say I'm going to fix the tranny but in the mean time have a 2002 GT to drive until I'm in the mood to start that job. I'm sure that I'll get to it before I need to replace the 2002 with a newer model but only time will tell.